Oscillating helicoidal separating device



March 14, 1961 T. J. GRAY OSCILLATING HELICOIDAL SEPARATING DEVICE Filed July 8, 1958 j INVENTOR THOMAS J. 624) OSCILLATING HELICOIDAL SEPARATING DEVICE Thomas J. Gray, Alfred, N.Y., assignor to Gulf Research 8 Development Company, Pittsburgh, Pa., :1 corporatlon of Delaware Filed July s, 1958, Ser. No. 747,248

11 Claims.- (Cl. 209-434 invention relates to an oscillating helicoidal separating device for separating particulate solid material, and more particularly it relates to a separating device comprising a plurality of superimposed non-rotating helicordal'surfaces, with means for oscillating each such surface independently at different amplitude and at different frequencyfrom the other helicoidal surfaces in the series, and having means for transfer of material-in-process through the series of helicoidal surfaces.

The separation of solid particles of various densities by means of vibrating and oscillating tables is well known. I have invented a new form of separating table which is a considerable improvement over earlier types in, that it takes advantage of different kinds of motion than has previously been used in separating tables, and in that'a higher degree of separation according to density is obtamed, much less space and much less power is required for any separation than has been the case with prior known types. My device also effects a large scale diminution in the requirement for floorspace and in size and cost of the buildings to house the equipmentfor any specific quantity of material to be handled. This saving in size and cost of buildings to house these devices is in itself a matter of much economic consequence.

This invention will be described in connection with the accompanying drawings, in which:

Figure 1 is'primarily an elevation view, partly in vertical section, showing the oscillating helicoidal separating device, 1

Figure 2 is a perspective view of the individual helicoids, bearing the part identification numerals which relate to the lowermost helicoid, and

Figure 3 is a perspective view of the axial sleeve which constitutes the central and supporting construction of the helicoid and it also shows the drive shaft of the device and the eccentric element mounted thereon.

Figure 4 is a sectional view showing details of another embodiment of my invention.

Referring to Figure 1, element. 11 is a vertical shaft 4 supported in frame 10. Surrounding shaft 11, in upper sections thereof, are concentric shafts 12 and 13. Shafts 11, 12, and 13 respectively, are fitted with eccentric sections 21, 22, and 23. The eccentric sections 21, 22, and 23 carry, respectively, oscillating helicoids 31, 32, and 33, the details of which are shown in greater detail in Figures 2 and 3. In each of elements 31, 32, and 33, the helicoidal surface is constructed around and rigidly fastened to sleeves or cores 41, 42, and 43. The helicoidal surfaces in each case are constructed in axial alignment with their sleeves 41, 42, and 43, and are so constructed that every radius of each helicoidal surface is at a 90 angle to the axis of its sleeve 41 42, and 43.

The weight of helicoid 31, with its integrally constructed sleeve 41 is supported from shaft 11 by means of collar 51. In a similar manner the lower end of shaft 12, and also helicoid 32, are supported from shaft 11 by means ofcollar 52. The lower end of concentric shaft 13, and also helicoid 33, through its sleeve 43, are supported from concentric shaft 12 by collar 53.

Concentric shafts 11, 12, and 13 respectively, are driven through pulleys 61, 62, and 63 and their respective belts 64, 65, and 66. v

Rotary motion of helicoids 31, 32, and 33 is prevented by tie rods 81, 82, and 83 extending from the perimeter of the helicoids to adjacent points on frame 10 or to other nearby fixed bodies. A tank or bin 88 is provided to hold the particulate material or slurry to be separated, and a pipe or chute 89 extends from the bottom of the said tank or bin to discharge onto an intermediate portion of the top helicoid, 33. A series of troughs 71 are-provided to conduct separated material from different points on the lower lip 86 of helicoid 31 (see Figure 2). -18, similar series 74 are provided to receive and deliver material discharged from the upper lip of helicoid 31. Similarly, a series of troughs 72 and receive and deliver material discharged from the lower and upper lips respectively of helicoid 32. A series of troughs or chutes 73 and 76 serve helicoid 33 precisely'as troughs 71 and 74 serve helicoid 31. A series of troughs 72 discharge onto the surface of helicoid 31 at various distances between the inside and the outside edge of the helicoidal surface, and a series of troughs 73 likewise conduct material from various points on the lower lip of helicoid 33 and discharge to intermediate points on the helicoid 32. Considerations of space have limited the number of troughs or chutes shown in each of the series 71, 72, 73, 74, 75, and 76, but any number of such troughs or chutes, either few or many, may be provided for each series, according to the material being processed and the number and closeness of cuts desired. Chutes 71, 74,- 75, and 76 may discharge into bags or other containers, not shown, or other means may be provided for conducting the material away from these discharge points. Drive shaft 11 is journaled solidly at its lower end in the frame 10, and this shaft, together with its snugly fitting concentric shafts 12 and 13 are journaled solidly in their upper sections by frame 10. i

While concentric shafts 12 and 13 are shown in Figure 1 extending downward from the top of frame 10,-th'ey could equally well be constructed to extend upward from the bottom of the frame 10 and be driven by pulley wheels positioned below the lowermost helicoid;

Referring to Figure 2, numeral 41 identifies the sleeve around which helicoid 31 is symmetrically constructed. In other words, helicoid 31 and its sleeve-core 41, are constructed in axial alignment with one another. Helicoidal surface 87 extends continuously from its upper extremity or lip at point through several turns to its lower extremity or lip at point 86. This helicoidal surface 87 is rigidly fastened throughout its length to sleevecore 41, and every radius of the helicoidal surface is at a 90 angle to the common axis of elements 31 and 41. Sleeve 41 has a concentric opening 6 from end to end, and eccentric element 21 fits snugly inside of opening 6. The helicoidal surface is surrounded by a standing rim 84 to add rigidity to the helicoidal surface and to pre- Vent the spilling of material ofi the outer edge. The upper and lower ends of the helicoidal surface, hereinafter spoken of as upper lip 85 and lower lip 86, do not have any raised rim. A tie 81 is fastened to the periphery of helicoid 31 at some point 7 and connects to 'a point 8 on frame 10 or on some other nearby fixed object. Tie 81 may be a spring, a cable, a chain, or a rod, and is provided to restrain any tendency of the helicoid to rotate. The foregoing description of Figure 2 is applicable not only to helicoid 31, but is similarly applicable, with corresponding identifying numerals, to helicoids 32 and'33 respectively.

The construction of the helicoid is shown further in partial section in the case of helicoid 33. That figure shows in section, concentric drive shaft 13, eccentric 23,

the sleeve-core 43, helicoidal surface 87 and upstanding rim 84.

Referring to Figure 3, the drawing shows vertical shaft 11, carrying eccentric section 21 and surrounded by sleeve 41 of helicoid 31. A helicoidal surface 87 is constructed around and rigidly attached to sleeve-core 41, as shown in Figures 1 and 2, but for clarity of presentation, the surface 87 is not shown in this figure. The eccentric element 21 may of course be constructed as a separate sleeve surrounding shaft 11 and keyed thereto. Eccentric element 21 has the same degree of eccentricity throughout its length. The degree of eccentricity of ele ments 21, 22, and 23 will ordinarily be such as to give a horizontal motion to helicoids 31, 32, and 33 of from 0.005 inch to 0.200 inch. The degree of eccentricity will be varied between eccentrics 2 1, 22 and 23 to give the greatest degree of eccentricity to the top helicoid 33 and the least degree of eccentricity to the lowest helicoid 31. The quoted horizontal motions of 0.200 inch and 0.005 inch are not given as specific figures to be used at the top and bottom of the series of helicoids, but rather 0.200 is the maximum at which the top helicoid will ordinarily be oscillated and 0.005 is the minimum at which the bottom-most helicoid 31 will ordinarily be oscillated. In any specific device, the number of superimposed helicoids in the series may be as low as two or three or any number in excess of three, but in every case the amplitude of the oscillations created by the eccentrics will be greatest at the top helicoid and will diminish successively to the lowest helicoid. The precise amplitude of oscillation provided for each helicoid by the eccentric elements 21, 22, and 23 will depend upon the specific material that. is to be separated, the diameter of the helicoid, and the position of the helicoid in its vertical series.

It should be noted that the degree of eccentricity of eccentrics 21, 22, and 23 is uniform throughout the length of the individual eccentric sections, and consequently there is no nutating motion of the helicoid and no vertical lift or float is given to the material being processed on the helicoidal surface.

The embodiment of my invention, certain details of which are shown in Figure 4, is constructedwith the same frame as shown in Figure 1, and has a vertical shaft 90 positioned similar to shaft 11 of Figure 1. However, vertical shaft 90 of Figure 4 is a non-rotating shaft. In this Figure 4, helicoidal surfaces 87 are indicated in broken section, constructed symmetrically about and rigidly fastened to a central sleeve or core 44. A hollow cylindric sleeve 91 is snugly fitted about non-rotating shaft 90, and is rotated by means of pulley wheel 67 and belt 68. The hollow cylindric sleeve 91 is supported by a collar 54'fastened to non-rotating shaft 90. Tightly fastened to sleeve 91 by means of a slot and key or other equivalent means is an eccentn'cally bored cylinder 24, corresponding to eccentric sections 21, 22,

and 23 of Figure l, which fits snugly and revolvably within helicoid core 44. Any number of helicoids may be mounted by this means along non-rotating shaft 90 supported in a frame such as 10.

In the operation of this device the helicoids 31, 32, and 33 of Figure l and 87 of Figure 4 do not rotate in any manner whatever, either about their own axes, about the axes of the several drive shafts, or about the axes of the eccentrics. But rather the axes of the several helicoids are, by means of eccentric sections 21, 22, and 23, and 24, revolved in small amplitude about the axis of drive shafts 11, 12, and 23 and 90, respectively. The resultis horizontal oscillation. The rotation of the eccentrics 21, 22, 23, and 24 inside of sleeves 41, 42,

'43, and 44 would tend to rotate sleeves 41, 42, 43, and

some portion of the helicoid, as indicated at 7 on Figure 2, to some fixed point on the surroundings of the device such as point 8 on the frame, as shown in Figures 1 and 2. 7

Although this device is well adapted to the separation of many different kinds of particulate material in which there are components of different densities, its operation with respect to finely divided ores is characteristic and its operation on finely divided columbium ore will be described.

In some instances the material to beseparated will be a mechanical mixture of different components characterized by different density, each individual particle being of uniform density throughout. In other cases, as in ores for instance, the ore will be crushed to such fineness as will approximate the foregoing condition. For instance, with columbium ore from Chewett in the Province of Ontario, Canada, an appropriate degree offineness is such as will pass through a standard 200 mesh sieve and be retained upon a standard 300 mesh sieve. It will ordinarily be desirable to pass this material over the separating device in the form of a slurry. For that purpose Water is quite satisfactory although it is advantageous that a defiocculating or wetting agent be present. Other conventional mediums, including mineral oil, are also effective in varying degrees with different materials.

The preferred slurry density when working with pyrochlore ore and when an aqueous medium is used, is of the order of 1.3 to 1.4. Separation is satisfactory in the case of slurries having densities below this range, but large throughput of liquid in proportion to solid reduces the efficiency of operation. Above this range, particularly with densities of 1.6 and upward in the case of pyrochlore, particle interaction is troublesome although differential wetting agents will sometimes extend the range somewhat.

Slurry is fed from tank 88 through conduit 89 to an intermediate section of the top helicoid 33. It is a characteristic of these helicoids that some of the material, usually the finest, will travel upward on the helicoidal surface while the remainder of the material tends to travel downward. The heaviest particles in their travel along the helicoidal surface work away from the central coreand out toward the periphery of the helicoidal surface. Consequently we are able to take off a multiplicity of cuts from the top lip of each helicoid and a multiplicity of cuts from the lower lip 86 of each helicoid. The number of cuts taken from each lip and the precise point at which they will be separated is determined according to the material being handled, the separation attainable in a specific case, and the degree of separation desired.

The quantity and character of material discharged from the top lip 85 of a helicoid will vary according to the direction of rotation of the drive shaft. Its rotation in one direction tends to urge some particles upward and its rotation in the opposite direction tends to urge the same particles downward. This also effects the throughput of the device.

Ordinarily, with oscillating separating devices for particulate material, high throughput gives poor separation, and good separation is attained only with low throughput. The outstanding characteristic of this device is that it gives a very high degree of separationeven at high rates of throughput. That characteristic is a consequence of having a succession of separating helicoids, with the successive helicoids operating at successively lower amplitude and successively greater frequency. That, of course, means that shafts 11, 12 and 13 are rotated at diiferent revolutions per minute, with shaft 11 giving the lowermost helicoid the highest frequency of oscillation, and shaft 13 giving the topmost helicoid the lowest rate of oscillation. As has previously been stated, the eccentric elements 21, 22, and 23 vary in degree of eccentricity to give the topmost ,helicoid the greatest amplitude of oscillation and to give the lowermost helicoid the least amplitude of oscillation.

The several cuts of material discharging from the bottom lip of helicoid 33 are conducted through troughs, chutes, conduits, or other conveying means 73 to an intermediate point of helicoid 32. They may be deposited onto helicoid 32 at different points on the radius of the helicoid, or they may be introduced onto the helicoidal surface at a single point as may be indicated by the degree of separation attained and the degree of separation desired. Further separation is effected on helicoid 32 precisely as it was effected on helicoid 33 except that the lower amplitude and the higher frequency of oscillation on helicoid 32 spreads out and sharpens the separation of particulate material on this helicoid.

Occasionally the separation effected on helicoid 33 has been suificiently thorough in part of the range to permit cutting one or more fractions from the bottom of helicoid 33 completely out of the separatory system. Whenever this can be done, as it frequently can, the throughput of the device is greatly increased.

The particulate material is separated on helicoid 32 exactly as has been described in respect of helicoid 33, and the product thereof is conducted by conducting means 72 to an intermediate point on helicoid 31. As previously described in relation to the material discharged from the lower lip of helicoid 33, that discharged from the lower lip of helicoid 32 will be taken off in such number of cuts and in cuts of such characteristics as desired, and those cuts may be delivered to such points on the radius of helicoid 31 as are found to give the best results. Again, some cuts from the bottom of helicoid 32 may be found to be separated to the requisite degree and may be removed from the separatory system without further handling on helicoid 31 and this operation, if possible, will give a further increase in capacity to the device. The final products from the downward progression will be finally removed from various points on bottom lip 86 of helicoid 31, the cuts again being such as are dictated by the degree of separation attained and the degree of separation desired.

As previously mentioned, some of the material chargedto a helicoid may travel up the helicoid in which case it leaves the upper lip 85 through discharge means 76, 75, and 74. Ordinarily the material which travels upward on the helicoid will be relatively small in volume and will be found to be well separated by the time it leaves the upper lip. In those cases Where it is found to not be sufiiciently separated the materials that have been discharged from the upper lips of two or more helicoids can be introduced to an intermediate point on a lower helicoid. However, when such an operation is performed, the helicoid onto which the material is discharged will sometimes advantageously be used solely for material discharged from upper lips. For instance, in a device having four superimposed helicoids, the descending material would be removed from the system at the lower lip of next to the lowermost helicoid, while the material discharged from the upper lips of the higher helicoids would be further separated on the bottommost helicoid.

The optimum diameter and number of turns of the helicoid, as well as the pitch, depend upon the material being separated; also on the desired rate of separation, the required degree of separation, the size of the particulate material, densities of the different particles and the difierence in densities between-various particles, all of these being obvious factors well known to those in the separatory arts. The amplitude and frequency of vibration are also important factors, as previously discussed. By way of actual useful dimensions, for moderate throughput, I have found that helicoids having diameters within the range of from one-and-a-half to four feet and having from one-and-a-half .to three full turns are particularly well suited for most separations. However, helicoids having only one full turn of 360 are fully adequate when a high rate of throughput is not required and when the pitch of the helicoid and the amplitude of oscillation are low and the frequency of oscillation is high. The use of helicoids having more than three full turns is desirable at times, particularly with helicoids of large diameter, high feed rates, and relatively high amplitude of oscillation. Helicoids of smaller diameter than oneand-a-half feet are quite satisfactory for small rates of throughput and I have found diameters substantially larger than four feet to be extremely effective and to give a high degree of separation together with an opportunity to successfully separate a greater number of cuts or fractions. Helicoids of larger diameter are generally most effective in the separation of relatively larger particles and ordinarily call for high amplitude of eccentricity. In the series of superimposed helicoids, the diameter, pitch, amplitude and frequency of oscillation, etc., of the various individual helicoids will be determined according to the work to be performed in each such st'age.

Under any one set of conditions the particles will travel outward only so far, and if the helicoid used is greater in radius than the travel of the particles it is perfectly feasible to omit raised rim 84 on the helicoid, assuming that the helicoid has sutlicient. rigidity without a rim. However, rigidity of the helicoid is most necessary and, if desired, the entire helicoid may be enclosed within a cylindric shell, this shell being fastened rigidly to the outer periphery of helicoidal surface 87 with requisite openings for feed lines. a

By way of specific information, for the previously described pyrochlore ore, a series of three helicoids, each having from one-and-a-half to two turns and pitches ranging from two to four inches, and having an amplitude of oscillation of approximately 0.15 inch and a frequency of 700 oscillations per minute on the top helicoid, and ranging down to the bottom helicoid with an amplitude of oscillation of 0.005 inch anda frequency of 1000 oscillations per minute has been found quite satisfactory. Such a device and operation have given mineral beneficiation ratios of 3 :1 and higher.

The amplitude and frequency of oscillation of the several helicoids in my device should be chosen according to the work to be done on each helicoidal surface. The separation of relatively larger particles will be improved with large amplitude of oscillation and moderate frequency, while the separation of relatively smaller particles will be opened up and improved by reducing the amplitude of oscillation and increasing the frequency of oscillation. It will ordinarily be found desirable to maintain the amplitude and frequency of oscillation as high as possible because a reduction of either of these factors reduces the throughput of the device. All factors must be adjusted according to their relative importance in the specific operation.

It will ordinarily be desirable to keep the amplitude of oscillation within the range of 0.200 inch to 0.005 inch, and the optimum ratio of amplitude of oscillation of the top helicoid to the amplitude of oscillation of the lowermost helicoid will not ordinarily exceed 30:1. In most cases it will not exceed 20: 1.

A frequency of oscillation of from 500 to 1200 per minute is the ordinary range for operation, the exact frequency being selected according to the various factors present in a specific instance. Lower frequencies, down to 300 per minute, will be efiective in many cases but needlessly reduce the capacity of the device. Frequencies as high as 2000 per minute have proven effective and satisfactory in the case of low throughput operation with very fine material.

A wide range of materials have proven satisfactory for the construction of the helicoidal surface. Stainless and other steels have proven satisfactory, rubber surface has proven satisfactory, and resin bonded fiberglass has 7 been highly satisfactory. When helicoidal surfaces are constructed of metal it is of the utmost importance that jointson the surface be fitted perfectly. Resin bonded fiberglass has a distinct advantage in that there need be no joints throughout the length of the helicoidal surface.

In the operation of this deviceheavy particles travel to the outside of the helicoidal surface while lighter particles tend to work toward the central core. Light particles are most frequently the ones which travel up the helicoid, but the reverse may be true if the helicoid has inadequate pitch for the particular material being han dled and the conditions of its operation. In choosing the pitch for a specific helicoid, the limiting condition is that the pitch shall not be great enough to cause turbulent fiow along the helicoid. The same limiting condition applies to the rate of charge from tank 88. I

In determining the point at which to introduce the slurry from tank 88 onto helicoid 33, and the points at which material will be discharged. by conductors 73 and 72 onto helicoids. 32 and 31, the likely place to start trials is at a point approximately 30 percent of the length of the helicoid from lip 85 and about 70 percent of the length of the helicoid from lip 86. These figures are a "rough approximation and the specific location will be selected as that at which it is possible to secure the most advantageous separation. That in turn will depend upon the densities of the various components of the particulate material charged, their size, the precise point at which the operator desires to cut the separation, and the direction of rotation of'the drive shaft with respect to the downward slope of the helicoid. A particular installation of a separating device such as the subject here described and claimed will in most cases be operating on about the same charge at all times and a few tests are the best guide to selection of specific dimensions and specific operating conditions.

Referring to the embodiment of my invention shown in certain detail in Figure 4, this device and its manner of operation correspond in all respects, except as elsewhere noted, with helicoids 31, 32, and 33 of Figure 1, and a series of any number of such helicoids can be constructed similar to the series of Figure 1 with corresponding 'feed means and corresponding intercommunicating troughs or chutes 71, 72, 73 and 74, 75, 76. This embodi- "ment of my invention is identical with that of Figure 1 except that the concent'ricshafts of Figure 1 are eliminated and the diameter of the core of the uppermost helicoid can thereby be reduced.

What I claim is:

1. An oscillating helicoidal separating device comprising a vertical drive shaft carrying a cylindric section eccentric to the axis 'of said shaft; a series of additional drive shafts in the form of hollow cylinders, the first of which being mounted concentrically and snugly about the first-mentioned drive shaft and the remaining shafts .of the said series being successively mounted concentrically and snugly about one another, with each successive shaft extending only a portion of the length of the next prior shaft in the series; on each individual drive shaft, positioned'adjacent one extremity of such shaft and at a point not surrounded by a hollow cylindric shaft, a

means for rotating the said shaft, and positioned adjacent the opposite extremity of each such shaft and at a point not surrounded by a hollow cylindric shaft, a cylindric section eccentric to the axis of said shaft; a hollow cylindric sleeve on each of said shafts, each'such cylindric sleeve fitting snugly and revolvably around the'eccentric section of the shaft to which it is fitted and being concentric with said eccentric section; a helicoidal surface of at least'one full turn constructed about each of the said hollow cylindric sleeves, in axial alignment therewith and rigidly fastened thereto, fitted with an upturned rim' throughout the length ofits-outer-edge but having no rim along its terminal lips; means for preventing rotation of the h eli'c'oidal surfaces; a 'rigi'cl frame I supporting the said vertical shafts; a means for supplying unseparated material to the uppermost of the several helicoidal surfaces; means for conveying separated material from the ,lower extremity of each helicoid except the lowermost to any selected portion of the next lower helicoid; means for discharging separated material from the lower extremity of the lowermost helicoid; and means for discharging separated material from the upper extremity of each helicoid.

dric section shall have a lesser degree of eccentricity than the next higher eccentric cylindric section.

3. The device of claim 1 in which every radius of each helicoidal surface is at an angle of 90 to the axis of the said hollow cylindric sleeve.

4. The device of claim 1 provided with a plurality of receiving means positioned below the terminal lip of each helicoid, adapted to receive separated material from different portions of the terminal lip.

5. An oscillating helicoidal separating device comprising a vertical drive shaft carrying a cylindric section eccentric to the axis of said shaft; a second drive shaft, in the form of a hollow cylinder, mounted snugly around and concentric with the first-mentioned drive shaft, extending only a portion of the length of the first-mentioned drive shaft; a third drive shaft, in the form of a hollow cylinder, mounted snugly around and concentric with the second drive shaft, and extending only a portion of the length of the second drive shaft; on each individual drive shaft, positioned adjacent one extremity of such shaft and at a point not surrounded by a hollow cylindric shaft, a means for rotating the said shaft, and positioned adjacent the opposite extremity of each such shaft and at a point not'surrounded by a hollow cylindric shaft, a cylindric section eccentric to the axis of said shaft; a hollow cylindric sleeve on each of said shafts, each such cylindric sleeve fitting snugly around the eccentric section of the shaft to which it is fitted; a helicoidal surface of at least one full turn constructed about each of the said hollow cylindric sleeves, in axial alignment therewith and rigidly fastened thereto, fitted with an upturned rim throughout the length of its outer edge but having no rim along its terminal lips; means for preventing rotation of the helicoidal surfaces; a rigid frame supporting the said vertical shafts; a means for supplying unseparated material to the uppermost of the several helicoidal surfaces; means for conveying separated material from the lower extremity of each helicoid except the lowermost to any selected portion of the next lower helicoid; means for discharging separated material from lower extremity of the lowermost helicoid; and means for discharging separated -material from the upper extremity of each helicoid.

'6. An oscillating helicoidal separating device which comprises a non-rotating vertical cylindric shaft; positioned along the length of said shaft a series of rotatable hollow cylindric sleeve members fitted snugly about said non-rotatable shaft and concentric therewith; a drive pulley attached to each of said rotatable sleeve members;

the helicoidal surfaces; a rigid frame supporting the said non-rotating vertical cylindric shaft; a means for supplying unseparated material to the uppermost of the several helicoidal surfaces; means for conveying separated material from the lower extremity of each helicoid except the lowermost to any selected portion of the next lower helicoid; :means for discharging separated :material from 2. The device of claim 1 in which each eccentric cylinthe lower extremity of the lowermost helicoid; and means for discharging separated material from the upper extremity of each helicoid.

7. The device of claim 6 in which each eccentric cylindric section shall have a lesser degree of eccentricity than the next higher eccentric cylindric section.

8. The device of claim 6 in which every radius of each helicoidal surface is at an angle of 90 to the axis of the said hollow cylindric sleeve.

9. The device of claim 6 provided with a plurality of receiving means positioned below the terminal lip of each helicoid, adapted to receive separated material from different portions of the terminal lip.

10. An oscillating helicoidal separating device which comprises a series of superimposed non-rotating helicoidal surfaces, means for oscillating each of said helicoidal surfaces independently at difierent amplitudes and at difierent frequencies from the other helicoidal surfaces, means for supplying unseparated material to the uppermost of the several helicoidal surfaces, means for conveying separated material from the lower extremity of each helicoid except the lowermost to any selected portion of the next lower helicoid, and means for discharging separated material from the lower extremity of the lowermost helicoid.

11. An oscillating helicoidal separating device which comprises a series of eccentrically bored cylinders arranged in vertically separated relationship, a hollow cylindric sleeve snugly and revolvably fitted about each of the said eccentrically bored cylinders, a helicoidal surface of at least one full turn constructed about each of said hollow cylindric sleeves in axial alignment therewith and rigidly fastened thereto, said helicoidal surface being fitted with a rim about the length of its outer edge but having no rim along its terminal lips, means for preventing rotation of the helicoidal surfaces, a means for supplying unsepa- References Cited in the file of this patent UNITED STATES PATENTS 829,443 Thurston Aug. 28, 1906 840,354 Lyle n Jan. 1, 1907 1,879,573 Sponable Sept. 27, 1932 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,974,799 March 14, 1961 Thomas J Gray It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 70, for "23 read 13 column 8, line 50, before "lower insert, the

Signed and sealed this 1st day of August 1961,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

